A built-in antenna apparatus for a Global Positioning System (GPS) of a portable terminal is provided. The apparatus includes a case frame for forming an exterior of the terminal, a main board fastened by the case frame and having a feeding portion and a ground portion of an antenna radiator, and an antenna radiator having a feeding point and ground point to be electrically connected to the feeding portion and ground portion of the main board, and is curved in a horizontal direction and a vertical direction of the terminal about a center of one upper-side corner of the terminal.